WO1991018847A1

WO1991018847A1 - Ceramic composite, process for producing it and its use

Info

Publication number: WO1991018847A1
Application number: PCT/EP1991/000980
Authority: WO
Inventors: Klaus Dreyer; Dieter Kassel; Hans Kolaska
Original assignee: Krupp Widia Gmbh
Priority date: 1990-06-01
Filing date: 1991-05-28
Publication date: 1991-12-12
Also published as: ATE115528T1; DE4028217A1; EP0532555B1; US5352533A; DE59103920D1; JPH05507462A; ES2067233T3; EP0532555A1

Abstract

The invention relates to a fibre-reinforced ceramic composite based on Al2O3, a process for manufacturing it and the use of the ceramic composite. To improve the mechanical properties such as bending resistance, fracture toughness and resistance to thermal shock, it is proposed that 0.05 to 10 wt. % of nickel and/or cobalt and/or iron be added. The ceramic composite is manufactured by a combined sinter/HIP treatment carried out in a heat without intermediate cooling. Special fields of application for the ceramic composite are automobile construction, gas turbines and cutting materials.

Description

description

Ceramic composite body, method for producing a ceramic composite body and its use

The invention relates to a fiber-reinforced ceramic composite body which contains the following components:

a) 5 to 40 mass% SiC hisker

bl) 0.05 to 3 mass% 2O3, Si0 ₂ , MgO, NiO and / or A1N and / or

b2) carbides, nitrides and / or carbonitrides of the metals of the IVa, Va or Vla group of the periodic table and / or oxides of the metals of the IVa group of the periodic table up to 40% by mass,

c) balance AI2O3 in a minimum amount of 30% by mass.

The invention further relates to a method for producing a ceramic composite body of the type mentioned, in which the starting powders are mixed, ground wet, dried, optionally granulated, pressed uniaxially or cold isostatically, and the composite body thus produced is sintered at 1450 ° C. to 1800 ° C. and then under a pressure of 5 to approx. 2000 bar is hot isostatically compressed (HIP).

The invention further relates to the use of the ceramic composite.

As described in DE-Z "ZWF", magazine for economic production and automation, 83rd year, pages 354 to 359, (1988), efforts to expand the field of application of ceramic cutting materials have recently led to the development of SiC- whisker-reinforced ceramics based on A ^^. The storage of SiC whiskers has a positive effect on his mechanical properties and performance when used as a cutting material. In particular, compared to whisker-free samples, whisker-containing samples have a significantly higher hardness, a higher toughness and a correspondingly lower risk of breakage.

In addition, EP 0 208 910 B1 proposes a fiber-reinforced ceramic material for tools which contains the following components:

(A) 50 to 60 wt% SiC fibers;

(B) 0.1 to 7 wt .-% of at least one oxide selected from the group consisting of CaO, MgO, SiC ^, NiO, ^sow ^ 2 ^ 3 *** - ^e lanthanide group consisting of; and at least one of the components (C) and (D), where

(C) 0.05 to 7% by weight of at least one component which is selected from a group comprising B, C, A1N, B ^ C and the borides of Si, Al, Y and lanthanum, and

(D) 0.05 to 40% by weight of a transition metal or oxide, carbide, nitride or boride thereof belonging to groups IVa, Va and via the periodic system of the elements, including solid solutions thereof, and

(E) balance AJ-2 3 in an amount of not less than 30% by weight.

It is the object of the present invention to improve the ceramic composite body mentioned above with regard to its mechanical properties. In particular, the fracture toughness, the flexural strength and the resistance to temperature changes are to be improved.

It is also an object of the present invention to achieve a suitable method to achieve the above-mentioned aim and to find a new use for the ceramic composite body according to the invention. This object is achieved in the fiber-reinforced ceramic composite body by the features specified in claim 1. Compared to the composite bodies known from the prior art, this body has 0.05 to 10% by mass of nickel and / or cobalt and / or iron (based on the total mass).

Preferably at least 0.4 to 3% by mass of nickel and / or cobalt and / or iron are used.

Comparably good strength properties are also obtained if up to 25% by mass of the nickel and / or cobalt and / or iron are replaced by chromium.

According to a development of the invention, up to 2% by mass of one or more noble metals can also be added to the ceramic composite body according to the invention. The noble metals are understood to mean the elements silver, gold, platinum, iridium, rhodium, ruthenium, palladium and osmium, platinum and / or palladium in particular being recommended in view of the better sintering properties.

According to a further embodiment of the invention, the proportion of SiC whiskers in the ceramic composite body according to the invention can be replaced in whole or in part, preferably up to 80% by mass, by SiC platelets.

The SiC whiskers and / or single-crystal SiC platelets can be used to improve the sinterability

(platelets) up to 2/3 of their total mass can be replaced by introduced SiC powder.

An improvement in the strength properties also results in the addition of zirconium or hafnium oxide or silicon nitride, which are incorporated into the Al2O3 matrix and make up up to 0 to 20% by mass (based on the total mass). Depending on the intended use, material improvement can be achieved by applying one or more hard surface layers, especially during machining. These surface layers, which are known in principle, consist of oxides, carbides, nitrides and / or carbonitrides of one or more of the elements of the IVa to Vla group of the periodic table and / or I2O3 and are applied by the likewise known CVD or PVD method.

The production of a ceramic composite body according to the invention is described in claims 9 to 14. An important new feature here is the sintering and hot isostatic gas pressure treatment (HIP) without intermediate cooling in a heat. This combined sintering / HIP process achieves a uniform structure.

In this process, the products according to the invention must preferably be sintered in an inert gas atmosphere or under vacuum and then subjected to a gas pressure treatment under an inert gas atmosphere, preferably an argon or nitrogen atmosphere. The temperature of the gas pressure treatment is chosen approximately equal to the sintering temperature or is up to 100 ° C lower.

When producing the mixture, it is important to introduce the metallic additives (iron and / or nickel and / or cobalt) in a very fine-grained form and to distribute them homogeneously in the mixture. For this, the powder mixture is e.g. mixed and ground in a drum mill for at least 48 hours with the addition of a grinding fluid. Acetone or i-propanol or preferably water can be used as the grinding liquid.

In order to obtain the most favorable possible distribution of the noble metal, it is preferably in the form of colloidal particles with crystallite sizes <20 nm uniform with the other components of the starting powder mixture mixed.

According to a further development of the invention, the noble metal is added as a colloidal hydrosol or colloidal lyosol in organic (acetone or i-propanol) or aqueous solutions.

A use of the ceramic composite material according to the invention will lie in particular in the case of bodies which are subjected to high thermal loads in an oxidizing and / or corrosive atmosphere, such as occur in particular in engines or in the gas turbine, or as cutting bodies for machining.

The ceramic composite body according to the invention with added iron is preferably used where only low corrosion resistance is required.

The improved mechanical properties of alloys according to the invention are explained below using exemplary embodiments. Show it:

Fig. 1 shows the bending strength

Fig. 2 shows the wear notch of an alloy according to the invention

3 shows the service life behavior in each case in comparison to an alloy known according to the prior art.

In a first exemplary embodiment, 88.5% Al ₂ O ₃ , 10.0% monoclinic ZrO ₂ , 0.5% SiO ₂ , 0.5% MgO, and 0.5% Ni - in each case in mass% - in pulverized form mixed and with the addition of water as a grinding medium for 48 hours in a drum mill.

In parallel, the SiC whiskers of a 6-hour deagglomeration and grinding in water in a drum cool subjected. After disagglomeration, the whiskers are classified by sieving to remove the coarse particles. The sediment can be processed after a rest period of approx. 10 hours.

The combined sieving / sedimentation process described removes remaining agglomerates and excessively long whiskers as well as the fine fraction. A fraction is used which mainly consists of whiskers with a length / diameter ratio of approx. 5 to 15. The selected whisker fraction is mixed with the matrix component described first in a ratio of 88:17 (matrix: whisker) in an aqueous suspension and homogenized in a drum mill for 2 hours. This is followed by drying in air at approx. 100 ° C and subsequent sieving of the dry cake to provide a finished powder mixture, which is too large in graphite molds. 150 to 300 mm is hot pressed at temperatures from 1300 ° C to 1800 ° C. Various inserts can be cut from these plates by cutting and grinding.

Instead of the hot pressing used here, alternatively the combined sintering / HIP production described in claims 9 ff. Can also be selected at whisker contents of up to 20% by mass, preferably 15% by mass.

1 shows the flexural strength of a l2θ3-Zrθ2 * ceramic reinforced with SiC whiskers with added nickel in comparison to a corresponding ceramic without metal parts. By adding 0.5% by mass of nickel, the bending strength could be increased from 740 N / mm ² to 800 N / mm ² .

2 shows the influence of the addition of nickel on the wear behavior of SiC-whisker-reinforced Al2θ -Zrθ2 * - ceramic. With a cutting speed V _c - 180 m / min, a cutting depth a_ = 1.5 mm, a feed f = 0.25 mm and a cutting time t _c = 6.3 min, the depth of the Wear notch, measured on the open area, when using a whisker-reinforced l2θ3 ~ Zrθ2 ceramic with 1% added nickel compared to a nickel-free whisker-reinforced ceramic with the appropriate composition reduced from 2.2 mm to 1.3 mm.

3, an aluminum oxide-zirconium dioxide ceramic with SiC whiskers without metallic additives, that is to say without nickel or cobalt or iron, was compared with a corresponding ceramic with 0.5% fine-grained cobalt. As can be seen from FIG. 3, the service life could be increased by more than 3 times by the addition of 0.5% cobalt. The cutting conditions are shown in Fig. 3.

The comparative ceramics with SiC whiskers used in each case had no metal components (Ni, Co, Fe), which increased the aluminum oxide proportion accordingly.

Claims

Patent claims

1. Fiber-reinforced ceramic composite body which contains the following components a) 5 to 40% by mass SiC whiskers bl) 0.05 to 3% by mass Y ₂ 0 ₃ , Si0 ₂ , MgO, NiO and / or AlN and / or b2) Carbides, nitrides and / or carbonitrides of the metals of the IVa, Va or Vla group of the periodic table and / or oxides of the metals of the IVa group of the periodic table up to 40% by mass, c) balance I2O3 in a minimum amount of 30% by mass , marked by

0.05 to 10% by mass of nickel and / or cobalt and / or

Iron.

2. Ceramic composite body according to claim 1, characterized in that 0.4 - 3% by mass of nickel and / or cobalt and / or iron are contained.

3. Ceramic composite body according to one of claims 1 to

2, characterized in that up to 25 mass% of the nickel and / or cobalt and / or iron are replaced by chromium.

4. Ceramic composite body according to one of claims 1 to

3, characterized in that up to 2 mass%, preferably up to 1 mass% - based on the total mass - of one or more noble metals (silver, gold, platinum, iridium, rhodium, ruthenium, palladium and osmium), in particular platinum and / or palladium are included.

5. Ceramic composite body according to one of claims 1 to

4, characterized in that the proportion of SiC whiskers is replaced in whole or in part, preferably up to 80% by mass, by SiC platelets.

6. Ceramic composite body according to one of claims 1 to

5, characterized in that the SiC whiskers and / or the single-crystalline SiC platelets up to 2/3 of their total mass are replaced by introduced SiC powder.

7. Ceramic composite body according to one of claims 1 to

6, characterized in that 0 to 20 mass% Zr0, Hfθ2 and / or

are included.

8. Ceramic composite body according to one of claims 1 to

7, characterized in that one or more surface layers consisting of oxides, carbides, nitrides and / or carbonitrides of one or more of the elements of the IVa to Vla group of the periodic table and / or Al2O3 are applied.

9. A method for producing a ceramic composite body according to one of claims 1 to 8, in which the starting powder mixture is mixed, wet ground, dried, optionally granulated, pressed uniaxially or cold isostatically and the composite body thus produced is sintered at 1450 to 1800 ° C. and then is hot isostatically compressed under a pressure of 5 to approx. 2000 bar (HIP), characterized in that the sintering and the HIP are carried out in a heat without intermediate cooling.

10. The method according to claim 9, characterized in that the sintering process of the combined sintering / HIP treatment is carried out in an inert gas atmosphere or under vacuum.

11. The method according to claims 9 and 10, characterized in that the gas pressure treatment of the combined sintering / HIP treatment in an inert gas atmosphere is preferably carried out in an argon or nitrogen atmosphere.

12. The method according to claims 9 to 11, characterized in that the HIP temperature is up to 100 ° C below the sintering temperature.

13. The method according to any one of claims 9 to 12, characterized in that the noble metal in the form of colloidal particles with crystallite sizes <20 nm is mixed uniformly with the other constituents of the starting powder mixture.

14. The method according to claim 13, characterized in that the noble metal is added as a colloidal hydrosol or colloidal lyosol in organic (acetone, i-propanol) or aqueous solutions.

15. Use of the ceramic composite material according to one of claims 1 to 8 as a material for thermally highly stressed bodies, in particular in automobile construction, in gas turbine construction or as a cutting body for machining.